diff options
Diffstat (limited to 'drivers/media/video')
| -rw-r--r-- | drivers/media/video/omap3isp/ispresizer.c | 40 |
1 files changed, 30 insertions, 10 deletions
diff --git a/drivers/media/video/omap3isp/ispresizer.c b/drivers/media/video/omap3isp/ispresizer.c index 40b2db873a13..70897ce5dced 100644 --- a/drivers/media/video/omap3isp/ispresizer.c +++ b/drivers/media/video/omap3isp/ispresizer.c @@ -714,16 +714,36 @@ static void resizer_print_status(struct isp_res_device *res) * iw and ih are the input width and height after cropping. Those equations need * to be satisfied exactly for the resizer to work correctly. * - * Reverting the equations, we can compute the resizing ratios with + * The equations can't be easily reverted, as the >> 8 operation is not linear. + * In addition, not all input sizes can be achieved for a given output size. To + * get the highest input size lower than or equal to the requested input size, + * we need to compute the highest resizing ratio that satisfies the following + * inequality (taking the 4-tap mode width equation as an example) + * + * iw >= (32 * sph + (ow - 1) * hrsz + 16) >> 8 - 7 + * + * (where iw is the requested input width) which can be rewritten as + * + * iw - 7 >= (32 * sph + (ow - 1) * hrsz + 16) >> 8 + * (iw - 7) << 8 >= 32 * sph + (ow - 1) * hrsz + 16 - b + * ((iw - 7) << 8) + b >= 32 * sph + (ow - 1) * hrsz + 16 + * + * where b is the value of the 8 least significant bits of the right hand side + * expression of the last inequality. The highest resizing ratio value will be + * achieved when b is equal to its maximum value of 255. That resizing ratio + * value will still satisfy the original inequality, as b will disappear when + * the expression will be shifted right by 8. + * + * The reverted the equations thus become * * - 8-phase, 4-tap mode - * hrsz = ((iw - 7) * 256 - 16 - 32 * sph) / (ow - 1) - * vrsz = ((ih - 4) * 256 - 16 - 32 * spv) / (oh - 1) + * hrsz = ((iw - 7) * 256 + 255 - 16 - 32 * sph) / (ow - 1) + * vrsz = ((ih - 4) * 256 + 255 - 16 - 32 * spv) / (oh - 1) * - 4-phase, 7-tap mode - * hrsz = ((iw - 7) * 256 - 32 - 64 * sph) / (ow - 1) - * vrsz = ((ih - 7) * 256 - 32 - 64 * spv) / (oh - 1) + * hrsz = ((iw - 7) * 256 + 255 - 32 - 64 * sph) / (ow - 1) + * vrsz = ((ih - 7) * 256 + 255 - 32 - 64 * spv) / (oh - 1) * - * The ratios are integer values, and must be rounded down to ensure that the + * The ratios are integer values, and are rounded down to ensure that the * cropped input size is not bigger than the uncropped input size. * * As the number of phases/taps, used to select the correct equations to compute @@ -799,10 +819,10 @@ static void resizer_calc_ratios(struct isp_res_device *res, max_height = min_t(unsigned int, max_height, MAX_OUT_HEIGHT); output->height = clamp(output->height, min_height, max_height); - ratio->vert = ((input->height - 4) * 256 - 16 - 32 * spv) + ratio->vert = ((input->height - 4) * 256 + 255 - 16 - 32 * spv) / (output->height - 1); if (ratio->vert > MID_RESIZE_VALUE) - ratio->vert = ((input->height - 7) * 256 - 32 - 64 * spv) + ratio->vert = ((input->height - 7) * 256 + 255 - 32 - 64 * spv) / (output->height - 1); ratio->vert = clamp_t(unsigned int, ratio->vert, MIN_RESIZE_VALUE, MAX_RESIZE_VALUE); @@ -870,10 +890,10 @@ static void resizer_calc_ratios(struct isp_res_device *res, max_width & ~(width_alignment - 1)); output->width = ALIGN(output->width, width_alignment); - ratio->horz = ((input->width - 7) * 256 - 16 - 32 * sph) + ratio->horz = ((input->width - 7) * 256 + 255 - 16 - 32 * sph) / (output->width - 1); if (ratio->horz > MID_RESIZE_VALUE) - ratio->horz = ((input->width - 7) * 256 - 32 - 64 * sph) + ratio->horz = ((input->width - 7) * 256 + 255 - 32 - 64 * sph) / (output->width - 1); ratio->horz = clamp_t(unsigned int, ratio->horz, MIN_RESIZE_VALUE, MAX_RESIZE_VALUE); |